Organic optoelectronic devices can utilize organic small molecules or polymers for conversion between light and electricity. For example, when transferred into their excited state by an external power source, organic active materials can produce light, therefore realizing an organic light emitting diode (OLED). On the other hand, active layers of organic photovoltaic (OPV) devices can utilize organic small molecules or polymers that produce energy upon exposure to light.
OLED devices may be referred to as polymer light emitting diode (PLED) devices or small molecule organic light emitting diode (SMOLED) devices depending on their active compositions. Earlier OLEDs were typically based on relatively simple structures, where a thin layer of the electroluminescence (EL) conjugated polymer was enclosed between a pair of electrodes. When a voltage is applied to the electrodes, the positive (anode) and the negative (cathode) electrodes can provide injection of holes and electrons, respectively, into the EL polymer. In the EL polymer layer, electrons and holes move towards each other in the applied electrical field and form excitons, which are bound excited states that can relax down into the ground state radiatively by emitting a photon. This process can be referred to as electroluminescence. ORGANIC OPTOELECTRONIC devices are of interest in, for example, display, signage, and lighting.
OLEDs were first designed in the 1980s. See, e.g., C. W. Tang, S. A. Van Slyke, Organic electroluminescent diodes, Appl. Phys. Lett. 1987, 51, 913. More recent developments in OLED materials and applications are generally described in Kraft et al., Angew. Chem. Int. Ed., 1998, 37, 402-428; and also in Z., Li and H. Meng, Organic Light-Emitting Materials and Devices (Optical Science and Engineering Series), CRC Taylor & Francis (Sep. 12, 2006). The disclosures of these references are incorporated by reference in their entirety.
In OPVs, the active layer can comprise a component that carries positive charge (or “holes”) and a second component that carries negative charge (or electrons), and a junction between the two components. The junction allows or facilitates the conversion of light to electricity. The electric charges can be collected by electrodes on each side of the device and can be used to used as a standalone power source or be connected to a power grid. In the photovoltaic device, one side of the active layer is typically transparent to allow light through to the active layer. The opposite side can have reflective elements to reflect light back to the active layer. Photovoltaic devices are important clean energy sources.